Doubled over with abdo pains 18wks

Help! I'm not usually a pessimist but over the last 2/3 days I've been getting on and off really strong abdominal pains, kind of like period pains but stronger and making me double over and takes my breath away.
Is this just trapped wind?! Or something more serious? I am getting worried as I have just been on a week's holiday up to Scotland and was lugging a rather heavy case. Anyone else got these symptoms?

Well its eased off a bit..... my friend who is also pregnant is hiring a foetal heart monitor off the internet, we're going to share the cost of it for a month its only £30. I think for peace of mind its really worth it, just to hear that little heart beating away will make me feel better. At least if I can have the reassurance that baby is still jumping around I will be able to handle the pains a little easier.............. thanks for your reply xxx

**** Update *******
The heart monitor which me and a colleague are sharing for one month's hire is GREAT! If anyone has the chance to hire one, go for it. I thought that the quality would be really poor but I heard the heartbeat as strong as ever.
Its great for that 'in between' waiting for scans, just a little reassurance that all is well in babyland!!!